Refuse burner for wood waste,bark residues,and other combustible solids

ABSTRACT

A conical or cylindrical burner for burning wood wastes, bark residues and other combustible solid wastes is disclosed which includes an insulating lining such as a refractory material applied over the inner surface of the shell of the burner to retard heat loss. The insulating liner may be applied in situ after erection of the burner shell. Rows of concentrically arranged grates provide means for delivering primary combustion air to the burning zone. The overfire and recirculation air system includes means to supply ambient and/or hot recirculating gases in a predetermined ratio to keep the burner temperature within a predetermined range. A temperature sensing means located near the exhaust opening at the top of the burner is operatively connected to a controller which automatically adjusts interconnected dampers in the ambient air and hot recirculating gas inlets of the overfire and recirculation air system to a ratio of ambient air to recirculated hot gases to maintain the burner temperature essentially constant even with variable fuel feed to the burner. The refuse burner is capable of combusting wood and bark residues efficiently with significantly reduced visible smoke and particulate matter.

United States Patent Leman [151 3,669,039 1' June 13, 1972 REF USE'BURNER FOR WOOD WASTE, BARK RESIDUES, AND OTHER COMBUSTIBLE SOLIDS Marvin J. Leman, Shelton, Wash.

[72] Inventor:

[73] Assignee: Simpson Timber Company, Seattle, Wash.

[22] Filed:- Aug. 27, 1970 211 Appl. No.5 67,522

[52] U.S.Cl.... ..l10/7A, l10/18R I [51 Int. Cl. F23g7/02 [58] FieldofSearch ..ll0/7,7A, I8

[5 6] References Cited UNITED STATES PATENTS,

2,530,208 11/1950 Sass ..1 10/18 2,804,031 8/1957 Douglass, Jr ....1 10/18 3,538,865 11/1970 Lusmann.... ....ll0/l8 2,592,491 4/1952 Toepel ..110/8 2,608,169 8/1952 Sparks et al ..1 10/18 X Ehrenzelleret'al ..l10/18 X Primary firaminer Kenneth W. Sprague Attorney-Seed, Berry & Dowrey ABSTRACT A conical or cylindrical burner for burning wood wastes, bark residues and other combustible solid wastes is disclosed which includes an insulating lining such as a refractory material applied over the inner surface of the shell of the burner to retard heat loss. The insulating liner may be applied in situ after erection of the burner shell. Rows of concentrically arranged grates provide means for delivering primary combustion air to the burning zone The overfire and recirculation air system includes means to supply ambient and/0r hot recirculating gases in a predetermined ratio to keep the burner temperature within a predetermined range. A temperature sensing means located near the exhaust opening at the top of the burner is operatively connected to a controller which automatically adjusts interconnected dampers in the ambient air and hot recirculating gas inlets of the overfire and recirculation air system to a ratio of ambient air to recirculated hot'gases to maintain the burner temperature essentially constant even with variable fuel feed to the burner. Therefuse burner is capable of combusting wood and bark residues efiiciently with significantly reduced visible smoke and'particulate matter.

9 Claims 5 Drawing Figures PATENTEDJUH 13 1912 SHEET 10F 3 MARVIN J. LEMAN INVENTOR ATTORNEYS PATENTEDJUH 13 m2 3, 669 0 3 9 sum 3 or 3 I I I ,i

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MARVIN J. LEMAN INVENTQR.

ATTORNEYS REFUSE BURNER FOR WOOD WASTE, BARK RESIDUES, AND OTHER COMBUSTIBLE SOLIDS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved refuse burner of the conical or cylindrical type.

2. Prior Art Relatingto the Disclosure Incineration of wood wastes and bark residues has generally been carried out by burning the wastes in conical or Wigwam burners. The typical Wigwam burner is a metal enclosure in the form of a truncated cone wherein wood wastes or bark residues are conveyed inside the burner and dropped onto a burning pile. Air is supplied to the combustion zone of the burner through a grate structure in the base of the burner. For the most part these wigwam burners have operated with little or no control and as a result the combustion efficiency of the burners has been very low. This has resulted in excessive smoke and particulate emissions neither of which is acceptable under many of the recently enacted state and federal air pollution regulations. A recent study (Wood and Bark Residue Disposal in Wigwam Burners, Stanley E. Corder et al., Bulletin 11, March 1970, published by the Forest Research Laboratory of the School of Forestry of Oregon State University) describes the results of a two year study of means of modifying Wigwam burners with particular attention to the prevention of air pollution. Modifications described by the study included a three-zone forced draft underfire system, a forced overfire air system with adjustable nonles natural draft vents, hot-gas receiving ducts, variable speed fuel conveyors and provision for adding auxiliary fuel. A temperature sensing system, such as described in US. Pat. No. 3,472,184 for sensing the temperature of the exit gases and controlling the amount of air to the underfire air system was also evaluated.

The emission standards for particulate matter in combustion of wood wastes and bark residues in many of the states where Wigwam burners are used specify that the burners operate with particulate emissions of 0.2 grains per cubic foot or less and a smoke capacity of Ringelmann No. 2 or less. One of the main problems in attaining these standards, particularly the standard relating to smoke capacity, has been the fact that most wigwam burners have operated at low temperatures with resultant low combustion efficiency and excessive smoke. It has been determined according to the study mentioned previously that operation of a Wigwam burner with exit-gas temperatures in the range of 700 to 900 F. results in minimum emissions of particulates, smoke and air pollutants. It has remained a problem, however, to design a practical burner capable of efficiently combusting wet wood wastes and bark residues so that the exiting combustion gases exit the burner at a temperature of 700 to 900 F. considering the variable fuel input generally necessary.

SUMMARY OF THE INVENTION This invention relates to a means of burning wood wastes and bark residues and other solid combustibles with improved efficiency and less air pollution. One or more layers of a material which reduces heat loss through the shell wall and prevents air leakage into the burner through openings in the shell wall are applied to the inner surface of the shell wall of a conical or cylindrical burner. Refractory insulation applied in situ is preferred. The under fire air system of the burner includes a plurality of grates mounted flush with the floor of the burner. Multiple grates are arranged into two or more concentric rows with a controlled, independent air supply to each of the concentrically arranged rows. The over fire and recircula tion air system includes means to supply ambient and/or hot recirculating gases in a predetermined ratio to keep the burner temperature within a predetermined range. To efficiently control combustion in the burner the temperature of the exit gases through the top ot the burner is sensed and the measured temperature used to control the ratio of ambient air to hot recirculated gases reinjected into the burner through the overflre air system.

It is a primary object of this invention to provide a refuse burner wherein a heat insulating material is applied to the inner surface of the shell wall of the burner.

It is a further object of this invention to provide a refuse burner for burning wood wastes, bark residues and other solid combustibles which is capable of efficient combustion and reduced air pollution.

It is a further object of this invention to provide an improved refuse bumer for burning wood wastes, bark residues and other solid combustibles wherein the temperature of the exit gases through the top of the burner is used to control the ratio of ambient air to recirculated gases supplied to the burner through the overfire and recirculation air system.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall side view of the wigwam burner of this invention;

FIG. 2 is a partial cross sectional view through the wall of the burner showing a material which retards heat loss applied to the inner surface of the shell wall;

FIG. 3 is a plan view of the burner of FIG. 1;

FIG. 4 is a plan view of the grate arrangement of the burner of FIG. 1; and

FIG. 5 is a cross sectional view of the grate arrangement and underfire system of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1 the refuse burner of this invention comprises in general a conical or cylindrical burner 10 made up of a plurality of steel plates fabricated into the form of a cone, a grate system 20, a forced air underfire system 30 for directing primary combustion air under pressure into the interior of the burner through the grate structures of the grate system 20, a forced air overfire and recirculation system for withdrawing hot gases from inside the burner, mixing the hot gases with ambient air and reinjecting the mixed gases into the interior of the burner, a temperature sensing means 50 operatively connected to a controller which is, in turn connected to dampers of the overfire and recirculation air system, and a variable speed conveyor 60 for conveying the material to be burned into the interior of the burner.

The shell 10 of the burner is of conventional construction and is generally formed of heavy gauge sheet metal plates 11 formed with ribs 12, the plates secured to a rigid frame structure. Exterior circular rings 13 assist in supporting the burner shell. Observation ports 16 providing visual access to the inten'or of the burner may be provided at spaced intervals around the shell so that an operator can visually determine the location and size of the burning pile of combustible wastes. An access door 17 (see FIG. 3) to the interior of the burner is also provided for cleaning and maintenance. Because a lining of heat insulating material, preferably a refractory lining, is applied to the inner surface of the burner, the strength of the burner shell should be stronger than those conventionally used because of the added weight. A screen 14 covers the exhaust opening at the top of the burner to catch particulate matter which may become entrained in the exhaust gases. As shown in FIG. 2 a lining 18 of an insulating material is applied to the inner surface of the burner shell. The insulating lining may be applied to the inner shell walls of new or existing refuse burners. The lining serves to retard heat loss through the shell wall of the burner and to prevent leakage of outside air into the interior of the burner through openings between the plates, a problem encountered with many older burners. The lining is applied to the overall inner surface of the shell wall or to the lower portion of the shell wall adjacent the burning zone. The lining is preferably a refractory lining conventionally applied after fabrication and erection of the shell wall or before. Gunnite grade castable refractory materials are suitable. The refractory material integral with the shell wall on the lower portion thereof is subjected to higher temperatures than is the shell wall above the burning zone. For this reason an insulating material of lesser quality can be applied to the upper portion of the shell wall, for example, calcium silicate or a thermo-asbestos type material. The lower portion of the lining, however, should be a high grade refractory material.

An additional advantage obtained by providing an insulating lining on the inner surface of the shell wall is that of operating at higher temperatures than is normally possible. Most refuse burners of the conical type are operated so that the exit gas temperatures are in the range of 600 to 1,000" F. With the insulating lining the refuse burner of this invention can operate at exit gas temperatures of 1,200 F. or greater without affecting the structural integrity of the burner shell and without severe oxidation of the inner surface of the steel plates. Generally refractory linings are applied through and over a wire mesh held in spaced relation from the inner surface of the shell by studs at spaced intervals. The thickness of the lining can be as needed and may be varied from top to bottom, the thicker lining applied to the lower portion of the shell.

The shell of the burner is rested on a base of concrete or other suitable material. The waste material to be burned is conveyed into the interior of the burner by suitable conveying means 60 as shown in FIG. 1. The wood wastes or bark residues are dropped in a pile on the floor of the interior of the burner, the floor incorporating a grate system through which air is supplied for combustion.

The grate system of the burner of this invention is shown in detail in FIG. 4 and comprises two or more concentric rings of grate boxes with each of the rings supplied with air independently of the other. The grate system of the refuse burner of this invention is designed to furnish the majority of the primary combustion air to the burning zone contrary to the design of the grate systems of previous refuse burners for burning wood fuels designed to furnish less than 50 percent of the primary combustion air. Considerably more grates are provided in the grate system of this invention to supply greater amounts of combustion air to the burning zone at reasonable air velocities. Grate boxes 21 are formed in the base 15 of the burner and connected by feed pipes 22 to their respective air ducts 23, 24, and 26. The grate boxes are arranged into a central circular set, an intermediate concentric circular row of grates and outer concentric, circular row of grates. Additional concentric rows can be provided if needed or desired. Air duct 23 connects with the feed pipes of the central set of grates. Air duct 25 connects with the feed pipes of the intermediate row of grates and air ducts 24 and 26 connect with one-half the feed pipes respectively, of the outer row of grates. Air flow to the outer row of grates is split so that, should the burning pile of wood wastes or other material shift to an off-center position, air flow through the half-ring not covered by the burning material can be terminated. Better control of the combustion air to the burning zone can thus be achieved. Each of the grate boxes is covered by a directional grating 27, preferably directing the air inwardly. The gratings are mounted flush with the floor of the burner for easy cleaning and removal of ashes and other waste products from the burning zone at predetermined intervals.

The underfire air system 30 supplying forced air to the grate system consists of one or more blowers 31 and 33 supplying air through suitable conduits to each of the concentric rings of the grate system 20. Blower 31 supplies air through conduit 32, to the central set of grates. Blower fan 33 supplies air through conduits 34, 35 and 36 to the intermediate and outer rings of grate boxes. Each of the blowers is of conventional construction and commercially available, the blowers powered by electric motors or other suitable means. Louevered dampers 37, 38, 39 and 40 are housed in each of the conduits 32, 34, 35 and 36 to independently control the relative amounts of air delivered to each of the rings of grates. Vanes 41 are housed in the air inlet of blower 33 to control the amount of air entering the blower. Each of the sets of louvered dampers is operatively connected to damper controls 42, 43, 44,45 and 46 respectively. These controls are motor operated and provide proportional control of the air delivered to the grate system. Blower 31 supplying combustion air to the central grates is used for fire startup and during burning. Combustion air is supplied to the intermediate and outer rings of grates as needed. When the fuel pile is relatively small air need only be supplied to the central and intermediate grates. As the size of the fuel pile increases air is supplied to the outer rings as needed. Additional rings of grates may be provided if needed.

The overfire and recirculation air system 70 is shown in FIGS. 1 and 3 and comprises means for removing hot gases from inside the burner, mixing the hot gases with ambient air from outside the burner and reinjecting the mixed air through adjustable nozzles. The nozzles can be adjusted so that the jets of air are directed approximately tangent to the shell of the burner or to the burning fuel pile. If the air flow through the nozzles is directed approximately tangent to the natural air flow the Corioulis effect is enhanced and the combustion efficiency of the burner increased due to the greater length of time the gases remain inside the burner. As shown in FIG. 3 blowers 71, 72 and 73 are spaced at regular intervals around the outside of the burner. More fans may be used if desired. Each blower has associated with it an air intake duct 74. Recirculation ducts 75, communicating with the interior of the burner intersect with each of the air inlet ducts at about a 45 angle. In each of the ducts, that is the air intake ducts and recirculation ducts, are housed adjustable louvered dampers 76 and 77 for controlling the ratio of ambient air to hot recirculated gases entering the burner through the overfire nozzle. The louvered dampers 76 and 77 are preferably interconnected so that when dampers 76 are open, dampers 77 are closed. Each of the sets of louvered dampers is operatively connected to a control 78.

The output of each of the blowers is through respective conduits 79 and adjustable nozzles 80. The nozzle can be made rotatable about a horizontal axis to change the slope of the fan-shaped jet of air to conform to the slope of the fuel pile and adjustable about a vertical axis to change the direction of the jet of air.

It has been determined smoke-free operation of a refuse burner of the type described results when the exit-gas temperature is in the range of 600 to 1,000 F. or higher. One of the advantages of the burner of this invention is a control system 50 capable of maintaining the exit gas temperature reasonably stable even with variable feed rates of fuel to the burner. The control system 50 includes a temperature sensing means 51 located near the burner exhaust opening. The sensing means 51 transmits a signal to temperature responsive control means 52 which, in turn, is operatively connected to motor-operated damper controls 78 which adjust the interconnect sets of louvered dampers 76 and 77 housed in the air inlet ducts and recirculation ducts to the correct ratio as desired to maintain the exit-gas temperatures within a predetermined range.

FIG. 1 illustrates a control panel having a temperature indicatorrecorder 91 operatively connected to the temperature sensing means 51, and a recording smoke density bolometer 92 for recording the density of smoke emission. Handoperated controls 93 are also provided for operating the motor-operated damper controls 42, 43, 44, 45 and 46. Conventional controls are also provided for starting and stopping the conveyor 60, the underfire air fans and the overfire and recirculation air fans. The motor-operated damper controls, the temperature responsive control means and the electric circuitry needed for connecting them are within the skill of the art. The control system 50 is connected so that the temperature responsive control means causes actuation of the motoroperated damper controls of each of the overfire and recirculation air systems to maintain the exit gas temperature, sensed by temperature sensing means 51, within a predetermined range. Ifdesired the ratio of overfire to recirculated air may be controlled manually instead of automatically.

OPERATION Fuel, consisting'of wet or damp wood wastes and bark residue, feedsinto the interior ofthe burner by conveyor 60 and drops in a conical pile on top of the grate system 20. The fire is-started manually and at the same time air is supplied to the underfire air system through the central grates of the grate structure by blower 31. Air through the remaining grates is added as the fire builds up. As the temperature rises the temperature sensor 51 records it on recorder 91. An operator or automatic controller 52 adjusts the ratio of hot recirculated gases to ambient air injected into the burner by the overfire and recirculation air system. The refractory lining or other heat insulating material applied to the inner surface of the shell of the bumer acts to substantially retard heat loss through the walls of the burner and thereby aids in attaining an overall higher combustion temperature, this higher temperature resulting in greater combustion efficiency, less particulate emission and less smoke emission. Use of the insulating lining also allows greater latitude in sizing of the burner.

When the temperature reaches a predetermined set point,

for example 850 F., the controller 52 responsive to the temperature sensing means 51 a (thermocouple, gas filled tube, etc. adjusts the dampers 76 and 77 and varies the ratio, of recirculated to ambient air through the overfire and recirculated air systemto maintain the temperature at the desired set point. The net result of the combination of heat-insulating lining, overfire air system and underfire air system with an independently controlled air supply to the grate systemresults in a burner having greater combustion efficiency with less smoke and particulate emission. The burner is capable of meeting existing as well. as forecast pollution regulations in the states where these burners are most utilized.

Iclaim:

l. A refuse burner for essentially, wood wastes; bark residues and other solid combustible wastes characterized by improved burning, reduced "amounts of particulates and smoke, comprising: v v a a base portion defining a floor for the burner,

a shell mounted on the base having an opening in the upper end thereof through which combustion gases exit into the atmosphere,

an integral lining of a refractory material covering the inner surface of the shell retarding heat loss through the shell and preventing air leakage into the burner through openings in the shell, an underfire grate system including a central circular set of grate boxes and one or more outer concentrically arranged sets of grate boxes around the central circular set, gratings covering each of the grate boxes mounted flush with the floor of the burner and having directional vanes therein,

separate air ducts providing combustion air under pressure to the respective sets of grate boxes, and

an underfire air system directing air under pressure through the grates of the grate system.

2. The refuse burner of claim 1 wherein the underfire air system includes conduit means providing air to each set of concentrically arranged sets of grate boxes independently of the other sets, air supply means for each of the conduit means, and damper means controlling the amounts of air delivered to the respective sets of multiple grate boxes.

3. The refuse burner of claim 2 including an independent air supply to essentially each half of the outer multiple grate boxes.

4. The refuse burner of claim 1 wherein the lining of material covers the entire inner surface of the shell.

5. The refuse burner of claim 1 including an overfire and hot gas recirculation system for removing predetemu'ned amounts of hot combustion gases at a plurality of locations around the perimeter of the shell above the burning zone of the burner, mixing the hot gases .with ambient air and re-injectingltlhe mixed ases into the bumer. Q

6. e refuse urner of claim 5 including heat sensing means positioned so as to be responsive to the temperature of the exit gases passing through the exhaust opening of the burner and control means operatively connected to the overfire and hot gas recirculation system and to the heat sensing means for varying the ratio of recirculated gases to ambient air injected into the burning zone by the overfire and hot gas recirculation system responsive to the temperature of the exit gases thereof. I

7. A refuse burner for essentially wood wastes, bark residues and other solid combustibles, comprising:

a base portion defining a floor for the burner,

a shell mounted on the base having an opening in the upper end thereof through which combustion gases exit into the atmosphere,

an integral lining of a refractory material covering the inner surface of the shell retarding heat loss through the shell and preventing air leakage into the burner through openings in the shell, I

an underfire grate system integral with the base through which primary combustion air is provided under pressure to the interior of the burner, I

an overfire and hot gas recirculation system for removing predetermined amounts of hot combustion gases at a plurality of locations around the perimeter of the shell above the burning zone of the burner, mixing the hot gases with ambient air, and reinjecting the mixture of gases into the burner,

heat sensing means positioned so as to be responsive to the temperature of the exit gases passing through the exhaust opening of the burner, and

control means operatively connected to the overfire and hot gas recirculation air system and to the heat sensing means for varying the ratio of recirculated gases to ambient air forced into the burning zone by the air system responsive to the temperature of the exit gases.

8. The refuse burner of claim 7 wherein the shell of the burner is in the form of a truncated cone.

9. The refuse burner of claim 7 wherein the underfire grate system includes a central circular set of grate boxes and one or more outer concentrically arranged sets of grate boxes around the central circular set, gratings covering each ofthe grate boxes, the grate boxes and gratings mounted so that the gratings are flush with the floor of the burner, directional veins in each of the gratings directing the incoming combustion air inwardly toward the center of the burner, and separate air ducts connecting to the central circular set and outer concentrically arranged sets of grate boxes through which air may be provided under pressure into the interior of the burner. 

1. A refuse burner for essentially wood wastes, bark residues and other solid combustible wastes characterized by improved burning, reduced amounts of particulates and smoke, comprising: a base portion defining a floor for the burner, a shell mounted on the base having an opening in the upper end thereof through which combustion gases exit into the atmosphere, an integral lining of a refractory material covering the inner surface of the shell retarding heat loss through the shell and preventing air leakage into the burner through openings in the shell, an underfire grate system including a central circular set of grate boxes and one or more outer concentrically arranged sets of grate boxes around the central circular set, gratings covering each of the grate boxes mounted flush with the floor of the burner and having directional vanes therein, separate air ducts providing combustion air under pressure to the respective sets of grate boxes, and an underfire air system directing air under pressure through the grates of the grate system.
 2. The refuse burner of claim 1 wherein the underfire air system includes conduit means providing air to each set of concentrically arranged sets of grate boxes independently of the other sets, air supply means for each of the conduit means, and damper means controlling the amounts of air delivered to the respective sets of multiple grate boxes.
 3. The refuse burner of claim 2 including an independent air supply to essentially each half of the outer multiple grate boxes.
 4. The refuse burner of claim 1 wherein the lining of material covers the entire inner surface of the shell.
 5. The refuse burner of claim 1 including an overfire and hot gas recirculation system for removing predetermined amounts of hot combustion gases at a plurality of locations around the perimeter of the shell above the burning zone of the burner, mixing the hot gases with ambient air and re-injecting the mixed gases into the burner.
 6. The refuse burner of claim 5 including heat sensing means positioned so as to be responsive to the temperature of the exit gases passing through the exhaust opening of the burner and control means operatively connected to the overfire and hot gas recirculation system and to the heat sensing means for varying the ratio of recirculated gases to ambient air injected into the burning zone by the overfire and hot gas recirculation system responsive to the temperature of the exit gases thereof.
 7. A refuse burner for essentially wood wastes, bark residues and other solid combustibles, comprising: a base portion defining a floor for the burner, a shell mounted on the base having an opening in the upper end thereof through which combustion gases exit into the atmosphere, an integral lining of a refractory material covering the inner surface of the shell retarding heat loss through the shell and preventing air leakage into the burner through openings in the shell, an underfire grate system integral with the base through which primary combustion air is provided under pressure to the interior of the burner, an overfire and hot gas recirculation system for removing predetermined amounts of hot combustion gases at a plurality of locations around the perimeter of the shell above the burning zone of the burner, mixing the hot gases with ambient air, and reinjecting the mixture of gases into the burner, heat sensing means positioNed so as to be responsive to the temperature of the exit gases passing through the exhaust opening of the burner, and control means operatively connected to the overfire and hot gas recirculation air system and to the heat sensing means for varying the ratio of recirculated gases to ambient air forced into the burning zone by the air system responsive to the temperature of the exit gases.
 8. The refuse burner of claim 7 wherein the shell of the burner is in the form of a truncated cone.
 9. The refuse burner of claim 7 wherein the underfire grate system includes a central circular set of grate boxes and one or more outer concentrically arranged sets of grate boxes around the central circular set, gratings covering each of the grate boxes, the grate boxes and gratings mounted so that the gratings are flush with the floor of the burner, directional veins in each of the gratings directing the incoming combustion air inwardly toward the center of the burner, and separate air ducts connecting to the central circular set and outer concentrically arranged sets of grate boxes through which air may be provided under pressure into the interior of the burner. 